diff --git a/css/build-css-testsuites.sh b/css/build-css-testsuites.sh
index 3ec72652f31daf..4aad0bbbb19e79 100755
--- a/css/build-css-testsuites.sh
+++ b/css/build-css-testsuites.sh
@@ -35,6 +35,7 @@ main() {
             exit 1
         fi
 
+        # The maximum Unicode code point is U+10FFFF = 1114111
         if [ `$PYTHON -c 'import sys; print(sys.maxunicode)'` != "1114111" ]; then
             echo "UCS-4 support for Python is required"
             exit 1